This invention relates to an input/output-signal checker for an electronic control unit in an electronically controlled fuel injection system for internal combustion engines, and more particularly to a checker of this kind which is capable of easily monitoring a plurality of input signals and a plurality of output signals, and also capable of promptly detecting and locating an abnormality and analyzing its cause.
Electronically controlled fuel injection systems in general for an internal combustion engine for vehicles are provided with an electronic control unit, which is supplied with various signals as input signals such as those representing engine operational parameters detected of engine rotational speed, absolute pressure in the intake pipe, engine coolant temperature, the throttle valve opening, and exhaust gas component concentration (e.g. oxygen concentration), to calculate the valve opening periods of fuel injection valves in response to these input signals, such that the air/fuel ratio of the mixture gas supplied to the engine becomes desired values appropriate to operating conditions of the engine, and also to supply driving signals corresponding to the calculated valve opening periods to the fuel injection valves. Through this control it is sought to improve engine performance and emission characteristics.
When some abnormality such as engine disorder occurs in a vehicle equipped with such an elecronically controlled fuel injection system as explained above, it is necessary to determine whether the abnormality is attributable to the electronic control unit itself, or input signals, or fuel injection valves, in order to find out the cause.
Conventionally, as inspection means to this purpose, a plurality of measuring instruments have been adopted, e.g. a synchroscope or an ammeter to inspect whether or not correct valve opening period signals are outputted from the electronic control unit, ordinary instruments such as a circuit tester to inspect the internal circuitry of the electronic control unit, and instruments to individually inspect such items as the interior of the other devices and the output signals therefrom. However, the electronic control unit is supplied with input signals of various engine operational parameters detected, and outputs valve opening period signals in response to these input signals. Therefore, the use of a plurality of instruments to individually inspect the electronic control unit itself and the input and output systems has made the inspection work too complicated and time-consuming.